Feed system

ABSTRACT

A radial-feed rotating drill tool having a tool holding fixture formed at an eccentric portion of a feed spindle eccentrically mounted in an external spindle. By rotating the feed spindle relative to the external spindle, a feed movement may be initiated with minimum expense. Further, because of the surface-contact mounting of the eccentric shaft portion of the feed spindle in the external spindle, mounting of the tool-holder without play is ensured.

[0001] The invention relates to a radial-feed rotating drill tool in accordance with the preamble of claim 1.

[0002] Feed systems of this kind are used in the series manufacture of case components, for instance of engine/transmission cases. The respective machining stations, for example transfer machines, fine-boring units, special machines, horizontal boring machines or machining centers are equipped with a feed system for boring tools in which the cutting tool is coupled with a work spindle of the machine tool via the feed system.

[0003] The feed system permits to compensate defects occurring during manufacture which may occur, for instance, due to the wear of cutting edges, cutting edge tolerance, adjusting errors or dimensional variations, caused by temperature changes of the machine, etc. Moreover the feed systems permit to form cylinder bores having most narrow tolerances or having bores the radius of which is variable in response to the boring depth (e.g. forming of chamfers, radii, recesses, convex, concave or tapered circumferential walls).

[0004] In the known systems the cutting tools may be formed on different tool holding fixtures, for instance boring bars, so-called eccentric spindles or feeding heads.

[0005] In EP 0 654 315 A1 a feed system is disclosed wherein an internal spindle is centrically mounted in an external spindle. The internal spindle carries at its face a control cam whereby a tool holder mounted on a face-side guide of the external spindle is displaceable in a radial direction so as to bring about a feed movement. The internal and external spindles may be driven independently of each other, so that a feed movement of the tool holder takes place when a rotational speed difference is provided. In the case of synchronously driven spindles no feed movement takes place.

[0006] It is a problem in this known solution that the tool holder must be guided both on the external and internal spindles, so that a considerable expense is required for guidance without play. All of the guide elements are formed on the face, so that the feed means requires a considerable construction space particularly in the radial direction.

[0007] In contrast, the invention is based on the object of furnishing a drilling tool wherein feeding is possible at minimum expenditure in terms of device technology.

[0008] This object is achieved by a drilling tool having the features of claim 1.

[0009] In accordance with the invention, the tool holding fixture is formed at an eccentric portion of a feed spindle which is eccentrically mounted in an external spindle. By rotating the feed spindle relative to the external spindle, a feed movement may be initiated with minimum expense. Owing to surface-contact mounting of the eccenter shaft portion of the feed spindle in the external spindle, mounting of the tool holder without play is ensured. The invention is characterized by a construction which is compact both in the radial and the axial directions, with the moved masses being minimum in comparison with the above described prior art.

[0010] In contrast, the invention is based on the object of furnishing a feed system for a rotating cutting tool and a process for controlling a like feed system, wherein accurate feed is possible at minimum expenditure in terms of device technology.

[0011] The use of rotation-symmetrical components moreover permits extremely high speeds both for the spindle and for the operating shaft so that high machining outputs can be realized.

[0012] Since the feed motion is effected solely due to a difference in speed between the operating shaft and the spindle, rapid feed motions can also be realized during the machining operation.

[0013] In addition to the radially adjustable cutting edge, the tool holding fixture is adapted to hold a further premachining tool which is preferably not adjustable by the feed system according to the invention.

[0014] Each of the spindle and the operating shaft can be driven via a belt drive or—as an alternative—can be directly coupled to the rotor of an electric motor, for instance a D.C. motor, a three-phase motor including a rotary frequency converter (for instance a three-phase asynchronous motor).

[0015] Other advantageous developments of the invention constitute the subject matter of the further subclaims.

[0016] A preferred embodiment of the invention will be described hereinafter in detail by way of schematic drawings, where:

[0017]FIG. 1 shows an embodiment of a drilling tool including an eccentric spindle,

[0018]FIG. 2 shows a diagram to illustrate the adjusting movement of the eccentric spindle, and

[0019]FIG. 3 is another drive variant for the embodiment of FIG. 1.

[0020] In the embodiment described in the following, the feed system is provided with a fine-boring tool by which, for instance, bearing bores of a bearing channel for crankshaft or camshaft bearings or the like can be machined.

[0021] In the FIGS. 1 and 2 an embodiment is illustrated in which a tool holding fixture, i.e a boring bar 32 is supported on an eccentric head. An eccentric head of this kind is principally known already from prior art so that merely some components essential for the invention have to be discussed hereinafter.

[0022] The drive of a feed spindle 25 and of a work spindle 6 is effected via drive motors 56 and 64, resp., which are connected to the feed spindle 25 and the spindle 6 through pulleys 90, 94 and 80, 84, resp., and synchronous belts 92 and 82, respectively. The latter, in turn, is run on rolling bearings 76, 77 in a spindle casing 78 which is fixed to the sliding drill head 68—also referred to as advance unit—. The axis of rotation of the spindle 6 is marked by M2 in the representation according to FIG. 1.

[0023] The feed spindle 25 is supported inside the spindle 6 and includes a drive shaft portion 120 at the end portion of which, shown on the right in FIG. 8, the synchronous pulley 90 and the supply 54 for the coolant/lubricant are formed. At the other end of the drive shaft portion 120 an internal bevel wheel 122 is formed which is in mesh with a corresponding external bevel wheel 124. The latter is formed on an eccentric shaft portion 126 of the operating shaft 25.

[0024] The drive shaft portion 120 extends coaxially with respect to the axis of rotation M2 and is run on rolling bearings 128 in the work spindle 6.

[0025] The eccentric shaft portion 126 is likewise run on adequate rolling bearings 130 in the spindle 6, wherein the eccentric center is marked by the axis M1. A continuous bore system 132 through which the coolant/lubricant can be guided from the supply 54 to the cutting edge 24 passes through the drive shaft portion 120 and the eccentric shaft portion 126.

[0026] On the face of the eccentric shaft portion 126 the boring bar 32 including a cutting tool 24 is mounted, i.e. the central axis of the boring bar 32 extends coaxially with respect to the axis M1 of the eccentric. The feed motion or variation of the adjustment of the cutting edge is effected by rotating the eccentric shaft portion 126 with respect to the work spindle 6 so that the radial distance between the axis of rotation M2 of the work spindle and the tool lip is varied due to the eccentricity. This adjusting movement is schematically represented in FIG. 2. M1 and M2 characterize the axes of rotation of the boring bar 32 and of the work spindle 6, respectively. An indexable insert 24 is fixed to the boring bar 32 and thus moves in the case of a relative rotation of the boring bar 32 vis-à-vis the work spindle 6 on the arc of a circle 130. By virtue of the distance e between the axes M1 and M2 the radial distance between the axis M2 of the work spindle and the tool lip varies in the case of this relative rotation. I.e. in the position marked by #1 the tool lip moves, with the spindle being driven, on a turning circle 132 having a comparatively large external diameter. When the eccentric shaft portion is adjusted by an angle α with respect to the work spindle, a turning circle 134 having a mean diameter can be adjusted and, in the case of a relative rotation about an angle β, a turning circle 136 having a smaller diameter can be adjusted.

[0027] In case that the adjustment of the cutting edge corresponds to the desired value, the work spindle 6 and the feed spindle 25—or more exactly the drive shaft portion 120 and eccentric shaft portion 126 thereof—are driven at the same speed so that there is no relative movement between the eccentric shaft portion 126 and the work spindle 6—the adjustment of the cutting edge is maintained and a bore having a constant diameter is formed.

[0028] For varying the bore diameter and for compensating production defects the speed of the feed motor 56 is varied, until a predetermined speed difference between the eccentric shaft portion 126 and the spindle 6 is brought about so that the aforedescribed adjusting movement is effected. After reaching this desired value, the work spindle 6 and the feed spindle 25 are again driven—as in the aforedescribed embodiment—at the same speed so that no relative displacement occurs between the eccentric and the spindle 6.

[0029] Such an eccentric spindle can principally be employed in response to the eccentricity for bore diameters of 10 mm or more.

[0030] The speeds of the spindle 6 and the operating shaft 25 are in turn sensed by sensors 72 and/or 62 by which an adequate control is effected. The control inputs for the feed and for the speed of the motors are generated, for instance, in an interpolator from the data detected by the sensors 62, 72, the geometry of the tool and the feed motion In the closed loop position controls operating as a follow-up system the desired actual position of the tool is adjusted via the mechanism of the sliding drill head and by an appropriate control of the drive motors. What is important is that the digital or analogous drive technology permits a conformal synchronous operation of the work spindle 6 and the operating shaft so that the desired size can be kept constant. The principle of construction including drive shafts guided inside each other (spindle, operating shaft) has a high rigidity which directly affects the tool lip by minimum excursions. As substantially rotationally symmetrical parts are used, the feed system according to the invention is also suited for high speeds. The dynamic boosters (feed motors 56, 64) permit rapid feed motions which can also be effected during the machining operation so that even a complicated bore geometry can be produced with high accuracy.

[0031] In FIG. 3 a drive for the drilling tool is indicated.

[0032] In the embodiment illustrated in FIG. 3, in which merely the part of the feed system on the drive side is shown, a belt drive is used for transmitting the driving torques of the feed motor 56 and the spindle motor 64, respectively.

[0033] The work spindle 6 is run on the rolling bearings 76, 77 in a case 78 mounted on the sliding drill head 68. At the end portion of the work spindle 6 which is stepped back in radial direction, shown on the right in FIG. 3, a synchronous pulley of the spindle is supported free from play which is driven by a synchronous belt 82 that, in turn, meshes with a driven pulley 84 of the spindle motor 64 arranged at a parallel distance from the axis of the spindle. The end portion of the feed spindle 25 shown on the left in FIG. 3 is run on rolling bearings 86 in the work spindle 6. The other end portion of the feed spindle 25 is supported by bearing arrangements which may be disposed in the area of the supply 54 for coolants/lubricants. Via this rotating supply 54 the coolant/lubricant can be guided through the axial bore 88 indicated in broken lines to the cutting edge.

[0034] In the area of the supply 54 a synchronous pulley 90 is fixedly connected to the feed spindle 25 which is in mesh with the driven pulley 94 via a synchronous belt 92 so that the driving torque of the feed motor 56 can be transmitted to the feed spindle 25.

[0035] The speeds of the synchronous pulley 80 of the spindle and the synchronous pulley 90 are sensed by sensors 72 and 62, resp., which are connected with the control unit for controlling the two drive motors 56, 64.

[0036] The construction represented in FIG. 3 has the advantage that the axial length of the feed system is small and that the synchronous belt drive constitutes a robust design which is easy to maintain and allows the use of standard parts as well as permits changes in the drive characteristic in a simple way even subsequently by exchanging the synchronous pulleys.

[0037] There is disclosed a feed system for a rotating cutting tool which is driven by a spindle and is adjustable in the feeding direction via an adjusting means. The adjusting means is driven by an operating shaft which can be driven synchronously with the spindle by a separate feed motor or at a predetermined difference in speed with respect to the spindle. In the case of a synchronous drive of the operating shaft and the spindle no feed is effected, whereas the cutting tool is adjusted, when a speed difference is adjusted by the adjusting means. After adjusting the desired position of the cutting tool, the operating shaft and the spindle are again driven at the same speed. 

What is claimed is:
 1. A feed system for a rotating cutting tool, comprising: a tool holding fixture adapted to be driven by a spindle; adjusting means moving the tool holding fixture in a feeding direction and including a control surface to which a transmission element is associated through which transmission element the tool holding fixture is translatable in a direction of adjustment in the event of a relative movement of the control surface with respect to the transmission element; wherein an internal spindle having an outer periphery at which the control surface is formed and which is adapted to be driven synchronously with the spindle or at a predetermined difference in speed with respect thereto by means of a feed motor.
 2. A feed system according to claim 1, wherein the internal spindle is guided in the spindle at least in portions.
 3. A feed system according to claim 1, wherein the tool holding fixture has the form of a boring bar coupled to the spindle, at an outer circumference of which a bending tool holder is fastened, and the transmission element is a radial pin passing through a circumferential wall of the boring bar and is biased against the control surface via a free end portion of the bending tool holder.
 4. A feed system according to claim 1, wherein the tool holding fixture is formed on a feeding head including a feeding head member guided in radial translation on a guiding head member arranged on the spindle, the internal spindle being adapted to be taken into contact with the transmission element arranged in the feeding head member through an intermediary of a portion thereof carrying the control surface.
 5. A feed system according to claim 4, wherein the feeding head member and the guiding head member are connected to each other through parallel springs.
 6. A feed system according to claim 4, wherein the feeding head member supports the boring bar.
 7. A feed system according to claim 1, wherein the control surface is formed at an outer circumference of a control member integrally connected to a drive member of the internal spindle.
 8. A feed system according to claim 1, wherein the control surface is curved in the form of an involute.
 9. A feed system according to claim 1, wherein the tool holding fixture supports a premachining cutting edge which is preferably not adjustable.
 10. A feed system according to claim 1, wherein each of the spindle and the internal spindle as an operating shaft are adapted to be driven via a belt drive.
 11. A feed system according to claim 1, wherein each of the spindle and the internal spindle as an operating shaft are coupled to a rotor of an electric motor.
 12. A feed system according to claim 2, wherein the tool holding fixture has the form of a boring bar coupled to the spindle, at an outer circumference of which a bending tool holder is fastened, and the transmission element is a radial pin passing through a circumferential wall of the boring bar and is biased against the control surface via a free end portion of the bending tool holder.
 13. A feed system according to claim 2, wherein the tool holding fixture is formed on a feeding head including a feeding head member guided in radial translation on a guiding head member arranged on the spindle, the internal spindle being adapted to be taken into contact with the transmission element arranged in the feeding head member through an intermediary of a portion thereof carrying the control surface.
 14. A feed system according to claim 5, wherein the feeding head member supports the boring bar.
 15. A feed system according to claim 2, wherein the control surface is formed at an outer circumference of a control member integrally connected to a drive member of the internal spindle.
 16. A feed system according to claim 12, wherein the control surface is formed at an outer circumference of a control member integrally connected to a drive member of the internal spindle.
 17. A feed system according to claim 13, wherein the control surface is formed at an outer circumference of a control member integrally connected to a drive member of the internal spindle.
 18. A feed system according to claim 3, wherein the control surface is curved in the form of an involute.
 19. A feed system according to claim 4, wherein the tool holding fixture supports a premachining cutting edge which is preferably not adjustable.
 20. A feed system according to claim 3, wherein each of the spindle and the internal spindle as an operating shaft are adapted to be driven via a belt drive. 